MICROBIOTA OF SEWAGE TREATMENT PLANTS AND 

 POLLUTED STREAMS 



By JOHN N. WILSON 



MINNESOTA DEPARTMENT OF HEALTH, MINNEAPOLIS, MINN. 



Late last century there was some controversy among sanitary engi- 

 neers in this country and in Eiirope concerning which of two methods of 

 sewage treatment should be advocated — chemical or biological treatment. 

 Those who favored the former tried to show that sewage could be treated 

 successfully in much the same manner as surface water is prepared for 

 drinking. However, the advocates of Mother Nature's method — biological 

 treatment — had caught a preliminary glimpse of her seemingly miraculous 

 powers of self-purification and were pressing ahead rapidly with their ex- 

 periments in this virgin field. In 1890, a report from the Lawrence Experi- 

 ment Station, in Massachusetts, stated that when sewage is passed intermit- 

 tently through a filter of coarse gravel from which all sand has been washed, 

 ". . . each stone was kept covered with a fine film of liquid, very slowly- 

 moving from stone to stone and continually in contact with air in the spaces 

 between the stones. The liquid, starting at the top as sewage, reached the 

 bottom within twenty-four hours with the organic matter nearly all burned 

 out" (Mills 1890) . Shortly after this report an English investigator, Scott- 

 Moncrieff (Anonymous 1892) , experimenting with the treatment of sewage 

 from his own home developed a filter plant using upward flow and demon- 

 strated beyond any doubt the biological action as opposed to mechanical 

 action alone. Although the early experiments in sewage treatment were con- 

 ducted largely by engineers, representatives of other professions, such as 

 bacteriologists, chemists, biochemists and biologists, began gradually to ap- 

 pear on the scene to contribute their share in the development of the methods 

 of biological treatment in use today. 



The purpose of this paper is to discuss sewage treatment from a biologi- 

 cal viewpoint and to show some relationships that exist between the micro- 

 biota of sewage treatment plants and polluted streams. The term microbiota 

 is used to designate those plants and animals which range from the higher 

 bacteria through certain aquatic insect larvae. In a sense, microbiota em- 

 bodies a synthesis of plankton (flowing sewage or polluted water of a 

 stream) and benthos (biological film of trickling filter or similar treatment 

 unit and bottom-dwelling organisms of a polluted stream) , Only those or- 

 ganisms which can be identified by direct microscopic examination are 

 included. The large group of bacteria which is commonly identified by 

 culture methods is omitted. 



To facilitate interpretation of the data, the microbiota of the sewage 

 treatment plants included in these studies have been divided into three 

 classes on the basis of function: The binding organisms, the free-living 



